Find out the error part of the following sentence;
The tutor cautioned (1)/ the girl's guardian (2)/ that she would not (3)/ be able to get through the examination until she works hard. (4)/ No error (5)

Explanation

until she works hard की जगह until she worked का प्रयोग होगा क्योंकि Reporting verb-cautioned Past Tense में है।